Page 174 - Physics Form 5 KSSM_Neat

A transformer that is in operation experiences a loss of
SCAN ME
energy. Therefore, the output power is less than the input power. SCAN ME
Sample
The efficiency of the transformer, h is defined as calculation for
ideal transformers
Output power
h = × 100%
Input power
http://bit.ly/2FVgecr
KEMENTERIAN PENDIDIKAN MALAYSIA
Nowadays, there are transformers with very high efficiencies, up to 99%. An ideal transformer
is a transformer that does not experience any loss of energy, that is the efficiency, h is 100%.

Output power
For an ideal transformer, efficiency of the transformer, h = × 100% = 100%
Input power
Therefore, output power = input power
V I = V I
P P
S S
Ways to Increase the Efficiency of a Transformer
The working principle of a transformer involves processes such as the flow of current in the
copper coils, the change of magnetic field and electromagnetic induction. These processes cause
loss of energy and the transformer is unable to operate at an optimum level. Most of the energy
is lost in the form of heat energy.

Activity 4.17 ISS ICS

Aim: To gather information and discuss the causes of energy loss in a transformer
Instructions:
1. Examine Table 4.9 that shows four main causes of energy loss and their effects.
Table 4.9
Causes of energy
Effects of energy loss
loss
Resistance of coils • The primary and secondary coils consist of wires that are very long.
• When current flows in the coils which have resistance, heating of the
wires occurs.
• Heating of the wires causes heat energy to be released to the surroundings.

Eddy currents • The changing magnetic field induces eddy currents in the iron core.
• The eddy currents heat up the iron core.
• The hot iron core releases heat energy to the surroundings.

Hysteresis • The iron core is magnetised and demagnetised continuously by the changing
magnetic field.
• The energy supplied for magnetisation is not fully recovered during
demagnetisation. The difference in energy is transferred to the iron core to
heat it up.

Leakage of • The magnetic flux produced by the primary current is not fully linked to the
magnetic flux secondary coil.

164 LS 4.3.2 4.3.3